The catalyst of this invention is suitable for the polymerization and copolymerization of ethylene and other 1-olefins, particularly of 2-8 carbon atoms, and the copolymerization of these with 1-olefins of 2-20 carbon atoms, such as propylene, butene and hexene, for example. It is well suited for economical particle form and gas phase polymerization processes. The active component of the catalyst is supported upon particles of an organic polymer, the selection of which affects the particle size, melt index and molecular weight distribution of the product polymer. Further, product bulk density is relatively high and is controllable by selection of the polymeric carrier.